A relay selection is introduced into a network which hybrids a cellular communication and a Device To Device (D2D) communication controlled by a cellular, and an idle user terminal serves as a relay for assisting in completion of the cellular communication between a base station and a destination user terminal, so as to enhance a diversity effect of the user terminal, improve data transfer rate, and improve data transfer stability; and user terminal relay communication is also a key research point on the D2D in future 5G communication.
In order to pursue global optimum, all the idle user terminals are often traversed in related technologies, to calculate corresponding selection criteria, and finally select the optimal relay user terminal, but a large computation cost results in great time delay of the system, so that the communication between the base station and the destination user terminal cannot be quickly established;
And in the related technologies, corresponding selection policy criteria is usually calculated based on user's instantaneous channel state information. Since the Channel State information (CSI) requires a large amount of feedback information, if state information of all the idle users is fed back to the base station, much channel bandwidth will be occupied, which results in a waste of resources;
In summary, there is still no effective solution in the related technologies for reducing resource consumption in establishing the relay communication, or improving efficiency of establishing a relay communication connection.